1. Field of the Invention
This invention is directed to a process for coating thermoplastic substrates with a coating composition that contains a non-aggressive solvent that does not attack the substrates and the process provides a finish that is smooth, even and free of defects and covers defects in the substrate.
2. Description of the Prior Art
Thermoplastic parts of ABS (acrylonitrile/butadiene/styrene), polyethylene, polypropylene, chlorinated polyolefins, polycarbonates, polyvinyl chloride and the like are widely used in automobiles and trucks and particularly in the interior of automobiles and trucks. Conventional coating compositions contain solvents such as toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone, propylene glycol monomethyl ether acetate and the like, which attack the surface of such thermoplastic parts. These conventional coating compositions when cured will telegraph any defects in the thermoplastic part or substrate. To hide such defects, a sealer is first applied and at least partially dried before a topcoat is applied. Another techniques that is used is to apply a layer of a conventional solvent based coating composition, allow it to cure, scuff or sand the resulting coating and then apply a second coating which usually hides the defects of the thermoplastic substrate.
Water borne coating compositions can be used which will not attack the thermoplastic substrate and when cured will not telegraph the defects of the plastic substrate through the coating as occurs with solvent based coating compositions in which the solvent attacks the plastic substrate. Typically, waterborne coatings do not provide the same high level of performance as do solvent based coatings.
It would be very desirable to utilize a solvent based coating composition to coat thermoplastic substrates that cures at ambient or relatively low temperatures in which the solvent of the composition will not attack the thermoplastic substrate and still be an excellent solvent for the coating composition and preferably not a regulated solvent which contributes towards air pollution problems.